The present invention relates to dye-based color ink sets having excellent color reproduction and lightfastness.
Images produced by ink compositions, when exposed to indoor or outdoor light beams, the open air for a long period of time, are frequently deteriorated due to an influence of ultraviolet and visible light, various gas in the air. In particular, in the case of color images produced by a plurality of ink compositions, the presence of even one color ink composition having poor lightfastness causes a change in hue of images, resulting in extremely deteriorated quality of color images. This has led to a demand for ink compositions capable of yielding highly weathering-resistant images which, even when stored for a long period of time, are less likely to be deteriorated.
Further, in recent years, attention has been drawn to ink jet recording. The ink jet recording is a printing method wherein droplets of an ink composition are ejected and deposited onto recording media, such as paper, to conduct printing. This method has a feature that images having high resolution and high quality can be printed at a high speed by means of relatively inexpensive apparatuses. Ink jet recording apparatuses utilizing this method are commercially widely accepted by virtue of good print quality, low cost, relatively quiet operation, graphics-forming capability. Among others, thermal (bubble jet) and piezoelectric drop-on-demand printers have been very successful on the market, and have been widely used as printers for personal computers for office and domestic applications.
In recent years, a method has become used wherein a plurality of color ink compositions are provided and used in the formation of color images by ink jet recording. In general, color images are formed using three colors of a yellow ink composition, a magenta ink composition, and a cyan ink composition, and optionally four colors of the above three color compositions plus a black ink composition. In some cases, six colors of the above four colors plus a light cyan ink composition and a light magenta ink composition are used in the formation of color images. What is required, of ink compositions for the formation of such color images is that they as such can exhibit good color development and, in addition, when used in combination with a plurality of ink compositions, can develop good intermediate colors.
Further, ink composition constituting ink sets used in this ink jet recording are required to have properties such that they have suitable property values, such as viscosity and surface tension values, have high optical density, can yield sharp color tone and images, can yield images having excellent fastness properties, such as excellent waterfastness and lightfastness, have excellent storage stability, and are less likely to cause nozzle clogging, are free from a problem associated with an odor, and are safe, for example, are free from the danger of fire. In order to satisfy a large part of these property requirements, water-base inks prepared by dissolving water-soluble dyes in water or in a mixed solution of water and a water-soluble organic solvent have been used. At that time, ink compositions having various hues are prepared from dyes having various hues.
Various image properties, such as color tone, lightfastness, and waterfastness, are greatly influenced by the properties of colorants in the ink compositions, and various dyes have hitherto been studied in the art, printing and photograph.
The present inventors have now found that ink sets comprising a combination of specific dye-based color ink compositions can realize images having excellent color reproduction and, at the same time, having excellent lightfastness. The present invention has been made based on such finding.
Accordingly, it is an object of the present invention to provide an ink set which can realize images having excellent color reproduction.
Thus, according to one aspect of the present invention, there is provided an ink set comprising: a yellow ink composition; two magenta ink compositions different from each other in color density, a magenta ink composition with higher color density and a magenta ink composition with lower color density; and two cyan ink compositions different from each other in color density, a cyan ink composition with higher color density and a cyan ink composition with lower color density,
said yellow ink composition containing as a colorant a compound represented by formula (I) or (II): 
xe2x80x83wherein
R1, R1xe2x80x2, R2, and R2xe2x80x2 each independently represent CH3 or OCH3; and
A and Axe2x80x2 each independently represent a group having a structure selected from the group consisting of 
xe2x80x83wherein
M represents a hydrogen atom, lithium, sodium, potassium, ammonium, or an organic amine; and
n is an integer of 1 or 2,
said magenta ink composition with higher color density containing as a colorant a compound represented by formula (III): 
xe2x80x83wherein
B and Bxe2x80x2 each independently represent a hydrogen atom or a group represented by formula 
xe2x80x83wherein
R2 represents OH, COOM, or NHR5 wherein R5 represents an SO3Mxe2x80x94 or COOH-substituted C1-C4 alkyl group;
R3 represents a hydrogen atom or an OHxe2x80x94 or COOH-substituted C1-C4 alkyl group; and
R4 represents an OHxe2x80x94, OCH3xe2x80x94, OC2H5xe2x80x94, SO3Mxe2x80x94, or COOM-substituted C1-C4 alkyl or phenyl group, provided that B and Bxe2x80x2 do not simultaneously represent a hydrogen atom;
R1 represents a C1-C4 alkyl or alkoxy group, OH, SO3M, or COOH; and
M represents a hydrogen atom, lithium, sodium, potassium, ammonium, or an organic amine,
said magenta ink composition with lower color density containing as a colorant the compound represented by formula (III) or a compound represented by formula (V): 
xe2x80x83wherein
x represents an anilino group substituted by at least one SO3M;
Y represents OH, Cl, or a morpholino group; and
M represents a hydrogen atom, lithium, sodium, potassium, ammonium, or an organic amine,
said cyan ink composition with higher color density and said cyan ink composition with lower color density each containing as a colorant a compound represented by formula (IV): 
xe2x80x83wherein
R6 represents OH or COOM; and
l, m, and n are each 0 to 4 with (l+m+n)=4.
According to another aspect of the present invention, there is provided an ink set comprising two magenta ink compositions different from each other in color density, a magenta ink composition with higher color density and a magenta ink composition with lower color density, the magenta ink composition with higher color density containing as a colorant the compound represented by formula (III), the magenta ink composition with lower color density containing as a colorant the compound represented by formula (V).
According to the ink set of the present invention, the presence of specific compounds as the colorant in the respective ink compositions can significantly improve the color reproduction of printed images and can yield images having improved lightfastness.
Ink Set
The ink set according to the present invention may be used in recording methods using an ink composition. Recording methods using an ink composition include, for example, an ink jet recording method, a recording method using writing utensils, such as pens, and other various recording methods. Preferably, the ink composition according to the present invention is used in the ink jet recording method.
The ink set according to the present invention basically comprises a yellow ink composition, two magenta ink compositions different from each other in color density, and two cyan ink compositions different from each other in color density. The two ink compositions different from each other in color, density may be divided into an ink composition with higher color density and an ink composition with lower color density.
Yellow ink composition
The yellow ink composition to be used in the present invention contains as a colorant a compound represented by formula (I) or (II). According to the present invention, compounds represented by formula (I) or (II) as the colorant may be used alone or as a mixture of two or more.
Specific examples of compounds represented by formula (I) or (II) include the following compounds. 
The concentration of the colorant in the yellow ink composition may be suitably selected. In general, however, the ink composition preferably contains 1.5 to 6.0% by weight of the compound represented by formula (I) or (II). This concentration range is preferred also from the viewpoint of the balance between the magenta ink composition and the cyan ink composition. Further, when the formation of blotted images (solid printing with 100% duty) on the so-called xe2x80x9cplain papersxe2x80x9d is carried out, the OD value of yellow is preferably in the range of 1.0 to 1.5. Therefore, the content| of the compound represented by formula (I) or (II) in the yellow ink composition is more preferably 1.5 to 4.0% by weight.
Magenta ink compositions
The two magenta ink compositions different from each other in color density to be used in the ink set according to the present invention are composed of a magenta ink composition with higher color density (hereinafter often referred to as xe2x80x9cdeep magenta inkxe2x80x9d) and a magenta ink composition with lower color density (hereinafter often referred to as xe2x80x9clight magenta inkxe2x80x9d). Ink jet recording using a deep magenta ink and a light magenta ink can provide recorded images having high sharpness and excellent lightfastness.
The magenta ink composition with higher color density to be used in the present invention contains as a colorant the compound represented by formula (III). The ink composition containing this compound as such, that is, when used in the formation of a single-color image, can yield images having excellent sharpness and lightfastness.
Specific examples of compounds represented by formula (III) include the following compounds. 
According to the present invention, compounds represented by formula (III) may be used alone or as a mixture of two or more.
When the compound represented by formula (III) is used in the light magenta ink described later, the magenta ink composition with higher color density preferably contains 1.5 to 3.5% by weight of the compound represented by formula (III). On the other hand, when the compound represented by formula (V) is used in the light magenta ink described later, the magenta ink composition with higher color density preferably contains 0.5 to 4.0% by weight of the compound represented by formula (III). According .to this preferred embodiment, when the formation of blotted images (solid printing with 100% duty) on the so-called xe2x80x9cplain papersxe2x80x9d is carried out, the OD value f magenta ink is in the range of 1.0 to 1.5.
According to the present invention, the colorant usable in the magenta ink composition with lower color density is the compound represented by formula (III) or (V). The compound represented by formula (III) to be used in the light magenta ink may be selected from the compounds as used in the deep magenta ink.
Specific examples of compounds represented by formula (V) include the following compounds. 
According to the present invention, compounds represented by formula (V) may be used alone or as a mixture of two or more.
The concentration of the colorant in the magenta ink composition with lower color density may be properly selected according to the color balance between the light magenta ink and the deep magenta ink used in combination with the light magenta ink. In general, however, when the compound represented by formula (III) is used in the light magenta ink, the light magenta ink preferably contains 0.2 to 0.9% by weight of the compound represented by formula (III). On the other hand, when the compound represented by formula (V) is used in the light magenta ink, the light magenta ink preferably contains 1 to 3% by weight of the compound represented by formula (V). When the compound represented by formula (III) or (V) falls within the above concentration range, the magenta ink composition with lower color density, when used in combination with the magenta ink composition with higher color density, can offer a good color balance between the deep magenta ink and the light magenta ink.
The combination of the above magenta ink compositions constitutes another aspect of the present invention. Thus, according to another aspect of the present invention, there is provided a magenta ink set comprising two magenta ink compositions different from each other in color density, a magenta ink composition with higher color density and a magenta ink composition with lower color density, the magenta ink composition with higher color density containing as a colorant the compound represented by formula (III), the magenta ink composition with lower color density containing the compound represented by formula (V). The magenta ink set according to the present invention may be used in combination with any ink composition without limitation. Specifically, for the magenta ink set, the formulations and the like may be the same as those of the magenta ink compositions described above, except that the, magenta ink set may be used in combination with a desired yellow ink composition, a desired cyan ink composition, and optionally a desired black ink composition. The magenta ink set according to the present invention can realize highly lightfast and sharp images.
Cyan ink compositions
The two cyan ink compositions different from each other in color density to be used in the ink set according to the present invention are composed of a cyan ink composition with higher color density (hereinafter often referred to as xe2x80x9cdeep cyan inkxe2x80x9d) and a cyan ink composition with lower color density (hereinafter often referred to as xe2x80x9clight cyan inkxe2x80x9d).
The cyan ink composition with higher color density and the cyan ink composition with lower color density to be used in the present invention each contain as the colorant the compound represented by formula (IV).
The difference in color density between the ink compositions different from each other in color density may be provided by using two ink compositions having different dye concentrations, or by properly selecting the types of colorants used.
Specific examples of compounds represented by formula (IV) include the following compounds. 
Regarding the colorant to be used in the cyan ink composition with higher color density and the colorant to be used in the cyan ink composition with lower color density according to the present invention, compounds represented by formula (IV) may be used alone or as a mixture of two or more.
The concentration of the colorant in the cyan ink composition with higher color density may be properly selected. In general, however, the cyan ink composition with higher color density preferably contains 2.0 to 6.0% by weight of the compound represented by formula (IV). Further, when the formation of blotted images (solid printing with 100% duty) on the so-called xe2x80x9cplain papersxe2x80x9d is carried out, the OD value of cyan is preferably in the range of 1.0 to 1.5. Therefore, the content of the compound represented by formula (IV) in the cyan ink composition with higher color density is more preferably 2.5 to 4.5% by weight.
The concentration of the colorant in the cyan ink composition with lower color density may be properly selected according to the color balance between the compound represented by formula (IV) used as the colorant and the deep cyan ink used in combination with the light cyan ink. In general, preferably, the cyan ink composition with lower color density contains 0.4 to 1.5% by weight of the compound represented by formula (IV). When the cyan ink composition with lower color density contains the colorant in the above concentration range, the cyan ink composition with lower color density, when used in combination with the cyan ink composition with higher color density, can offer a good color balance.
Black ink composition
According to the present invention, the link set comprising a yellow ink composition, two magenta ink compositions different from each other in color density, and two cyan ink compositions different from each other in color density may further comprise a black ink composition.
Any dye or pigment capable of yielding a black print may be used as a colorant contained in the black ink composition according to the present invention. Such dyes include, for example, various dyes commonly used in ink compositions, especially used in ink jet recording, such as direct dyes, acid dyes, foodstuff dyes, basic dyes, reactive dyes, disperse dyes, vat dyes, soluble vat dyes, and reactive disperse dyes. Such pigments include black pigments such as carbon black.
The black ink composition according to the present invention is preferably water-base inks from the viewpoint of safety and the like.
According to the present invention, these dyes may be contained, either alone or as a mixture of two or more, in the black ink composition.
Water, water-soluble organic solvent, and other optional ingredients
In the ink compositions to be used in the present invention, water or a mixed solution composed of water and a water-soluble organic solvent is suitable as a main solvent. Water may be pure water obtained by ion exchange, ultrafiltration, reverse osmosis, distillation or the like, or ultrapure water. Further, water, which has been sterilized by ultraviolet irradiation or by addition of hydrogen peroxide, is suitable because, when the ink composition is stored for a long period of time, it can prevent the growth of mold or bacteria.
In the ink compositions to be used in the present invention, when water is used as the main solvent, the water content is preferably 50 to 90% by weight, more preferably 60 to 80% by weight, based on the ink composition.
The solvent in the ink compositions to be used in the present invention is a mixed solution composed of water and a water-soluble organic solvent. Preferably, the solvent further contains a wetting agent comprising a high-boiling organic solvent. Preferred examples of high-boiling organic solvents usable herein include: polyhydric alcohols, such as ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, polypropylene glycol, propylene glycol, butylene glycol, 1,2,6-hexanetriol, thioglycol, hexylene glycol, glycerin, trimethylolethane, and trimethylolpropane; alkyl ethers of polyhydric alcohols, such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol monomethyl ether acetate, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol mono-n-propyl ether, ethylene glycol mono-iso-propyl ether, diethylene glycol mono-iso-propyl ether, ethylene glycol mono-n-butyl ether, ethylene glycol mono-t-butyl ether, diethylene glycol mono-n-butyl ether, triethylene glycol mono-n-butyl ether, diethylene glycol mono-t-butyl ether, 1-methyl-1-methoxybutanol, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol mono-t-butyl ether, propylene glycol mono-n-propyl ether, propylene glycol mono-iso-propyl ether, propylene glycol mono-n-butyl ether, dipropylene glycol mono-n-butyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol mono-n-propyl ether, and dipropylene glycol mono-iso-propyl ether; urea; 2-pyrrolidone and N-methyl-2-pyrrolidone; 1,3-dimethyl-2-imidazolidinone; formamide; acetamide; dimethyl sulfoxide; sorbit; sorbitan; acetin; diacetin; triacetin; and sulfolane. They may be used alone or in combination of two or more. Specific examples of preferred acetylene glycol surfactants usable in the present invention include compounds represented by the following formula (a): 
wherein 0xe2x89xa6m+nxe2x89xa650; and R1, R2, R3, and R4 each independently represent an alkyl group (preferably an alkyl group having 1 to 6 carbon atoms).
Among the compounds represented by formula (a), particularly preferred compounds include 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 3,6-dimethyl-4-octyne-3,6-diol, and 3,5-dimethyl-1-hexyn-3-ol. Commercially available products may also be used as the acetylene glycol surfactant represented by the formula (a). Specific examples thereof include Surfynol 82, Surfynol 104, Surfynol 440, Surfynol 465, Surfynol 485, and Surfynol TG (all the above products being available from Air Products and Chemicals Inc.) and OLFINE STG and OLFINE E 1010 (tradenames: manufactured by Nissin Chemical Industry Co., Ltd.).
The amount of the surfactant added is preferably about 0.1 to 3% by weight, more preferably about 0.5 to 2% by weight, based on the ink composition. The surface tension of the ink compositions to be used in the present invention is generally not more than 45 mN/m, preferably about 25 to 40 mN/m.
If necessary, the ink compositions to be used in the present invention may further containing nozzle clogging preventives, preservatives or antimolds, antioxidants, electric conductivity adjustors, pH adjustors, solubilizers, viscosity modifiers, penetrants, surface tension modifiers, oxygen absorbers, etc.
Examples of preservatives or antimolds include sodium benzoate, pentachlorophenol sodium, 2-pyridinethiol-1-oxide sodium, sodium sorbate, sodium dehydroacetate, and 1,2-dibenzothiazolin-3-one (Proxel CRL, Proxel BDN, Proxel GXL, Proxel XL-2, and Proxel TN, manufactured by Zeneca).
Examples of pH adjustors, solubilizers, or antioxidants usable in the ink compositions include: amines, such as diethanolamine, triethanolamine, propanolamine, and morpholine, and modification products thereof; inorganic salts, such as potassium hydroxide, sodium hydroxide, and lithium hydroxide; ammonium hydroxide; quaternary ammonium hydroxide, such as tetramethylammonium; salts of carbonic acid, such as potassium carbonate, sodium carbonate, and lithium carbonate; salts of phosphoric acid, such as potassium phosphate, sodium phosphate, and lithium phosphate; N-methyl-2-pyrrolidone; urea compounds, such as urea, thiourea, and tetramethylurea; allophanates, such as allophanate and methyl allophanate; biurets, such as biuret, dimethylbiuret, and tetramethylbiuret; and L-ascorbic acid and salts thereof.
According to the present invention, the other optional ingredients may be used alone, or alternatively a plurality of optional ingredients may be selected from the same category or different categories and used as a mixture.
According to the present invention, for each ink composition, the amounts of all the ingredients are preferably selected so that the ink composition has a viscosity of less than 10 mPaxc2x7s at 20xc2x0 C.
Recording Method
The ink set according to the present invention may be used in a recording method comprising the step of depositing an ink composition onto a recording medium to perform printing.
According to still another aspect of the present invention, there is provided an ink jet recording method comprising the steps of: ejecting droplets of an ink composition contained in the ink set according to the present invention; and depositing the droplets onto a recording medium to perform printing.
According to a further aspect of the present invention, there is provided a record produced by any one of these recording methods.